Aluminum bronze alloy having improved mechanical properties at elevated temperatures

ABSTRACT

AN ALUMINUM BRONZE ALLOY HAVING HIGH RESISTANCE TO INTERGRANULAR OXIDATION AND IMPROVED DUCTILITY AT ELEVATED TEMPERATURES. THE ALLOY COMPRISES FROM 5 TO 8% BY WEIGHT OF ALUMINUM, FROM 1.6 TO 2.9% BY WEIGHT OF IRON, FROM 0.005 TO 0.69% BY WEIGHT OF TIN, SILVER OR MIXTURES THEREOF, FROM 0.02 TO 0.14% VANADIUM, FROM 0.05 TO 0.5% BY WEIGHT OF ZIRCONIUM AND THE BALANCE COPPER. IN THE ALLOY COMPOSITION THE VANADIUM AND ZIRCONIUM COOPERATE TO PROVIDE IMPROVED DUCTILITY AS WELL AS STRENGTH AT ELEVATED TEMPERATURES.

United States Patent O 3,725,056 ALUMINUM BRONZE ALLOY HAVING IMPROVED MECHANICAL PROPERTIES AT ELEVATED TEMPERATURES Quentin F. Ingerson, Wauwatosa, Wis., assignor to Ampco-Pittsburgh Corp., Milwaukee, Wis. N Drawing. Filed Feb. 25, 1971, Ser. No. 119,001 Int. Cl. C22c 9/00 US. Cl. 75154 4 Claims ABSTRACT OF THE DISCLOSURE An aluminum bronze alloy having high resistance to intergranular oxidation and improved ductility at elevated temperatures. The alloy comprises from 5 to 8% by weight of aluminum, from 1.6 to 2.9% by weight of iron, from 0.005 to 0.69% by weight of tin, silver or mixtures thereof, from 0.02 to 0.14% vanadium, from 0.05 to 0.5% by weight of zirconium and the balance copper. In the alloy composition the vanadium and zirconium cooperate to provide improved ductility as well as strength at elevated temperatures.

BACKGROUND OF THE INVENTION This invention relates to an alpha phase aluminum bronze alloy having high resistance to intergranular oxide tion as well as improved hot ductility.

U.S. Pats. 2,829,969, 2,829,968 and 2,829,971 relate to an alpha phase aluminum bronze containing the addition of tin, silver or mixtures of tin and silver, Which act to prevent intergranular oxidation when the alloy is subjected to stress in a hot water or steam atmosphere. The term intergranular oxidation refers to the spontaneous cracking of an alloy when exposed to a corrosive media and to residual or applied stress.

While an aluminum bronze alloy as described in the aforementioned United States patents has good workability at normal temperatures, it has been found that at high temperatures the alloy has a tendency to be hot short due to a substantial decrease in ductility at a temperature range of about 900 to 1400 F. This decrease in ductility in this temperature range can produce cracking during working along the grain boundaries. As a result, alloys of this type are limited to the amount of working they can undergo at elevated temperatures.

It is also known that the addition of zirconium can improve the hot ductility and workability of certain copper base alloys as described in the British Pat. 1,144,344, in that the zirconium concentrates at the grain boundaries in the form of relatively large diameter zirconium atoms.

SUMMARY OF THE INVENTION The invention is based on the discovery that the hot ductility of alpha base aluminum bronze alloys containing the addition of tin, silver, or the combination of tin and silver, can be further improved by the addition of small amounts of vanadium and zirconium. The vanadium and zirconium cooperate to reduce the grain size and this acts to increase the ductility and prevent surface cracking during hot working, as well as increasing the strength at elevated temperatures.

DESCRIPTION OF THE PREFERRED EMBODIMENT According to the invention, the alloy has the following general composition range in weight percent:

Percent Aluminum 5.0 to 8.0 Iron 1.6 to 2.9 Tin or silver or mixture thereof 0.005 to 0.69

3,725,056 Patented Apr. 3, 1973 Percent Zirconium 0.05 to 0.50 Vanadium 0.02 to 0.14 Copper Balance The preferred compositional range of the alloy is as follows in weight percent:

Specific illustrations of alloys falling within the above ranges are as follows in weight percent:

Aluminum- 6.78 6.51 6.80 6.65

. l6 12 0. 11 Zirconium 0. 18 0. 13 Copper 90. 40 53 89.95 90. 64

The iron is employed in the above composition as a grain stabilizer and also acts to increase the strength of the alloy particularly at higher temperatures. In most cases the iron is employed in a ratio of about 1:3 with respect to the aluminum and this ratio provides the alloy With the most desirable grain refining characteristics and mechanical properties.

The tin and/or silver acts to increase the resistance of the alloy to intergranular oxidation, particularly when the alloy is subjected to stress in hot Water or steam atmosphere. This resistance to oxidation is believed to be brought about by the low heat of formation of the oxides of tin and silver, and thus the grain boundaries of the aluminum bronze alloy containing tin and/ or silver show unusual resistance to intergranular attack when stressed in steam or hot water media.

The addition of zirconium serves to improve the hot ductility of the alloy at elevated temperatures and particularly in the range of about 800 F. to 1400 F.

The vanadium serves to reduce the grain size of the alloy and substantially improves the hot working characteristics of the alloy. The vanadium cooperates with the zirconium to improve the ductility of the alloy at elevated temperatures and to increase the capability of the alloy to withstand cracking when subjected to rolling or other working in the temperature range of 800 to 1400 F.

Age hardening elements, such as silicon, beryllium, and the like, should be avoided in the alloy composition. Nickel, if used alone in aluminum-iron-copper alloys, will not age harden, but if combined with silicon, for example, the combination will age harden when the alloy is heated during welding or forming to form nickel silicides which are brittle and tend to precipitate at the grain boundaries. Therefore, age hardening constituents should be avoided in the present alloy.

The alloy is preferably formed by initially preparing a pre-alloy of copper, aluminum and iron. This pre-alloy is then alloyed with additional copper, tin and/or silver, vanadium and zirconium and cast. The resulting alloy can be readily fabricated into the form of rods, sheets, plate, tube, etc., or can be used as a weld deposit.

The alloy has improved mechanical properties, particularly ductility, at elevated temperatures. For example, the alloy has a percent elongation above 15% throughout the entire temperature range up to 1600 F. and has a tensile strength above 20,000 psi. at temperatures up to 1100 F. Thus, both the ductility and tensile strength of the alloy are substantially improved over similar alloy compositions, but without the addition of vanadium or zirconium, particularly in the temperature range of about 600 to 1600 F.

Various modes of carrying out the invention are contemplated as being Within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is the invention:

I claim:

1. An aluminum bronze alloy consisting essentially by weight of 5.0% to 8.0% aluminum; 1.6% to 2.9% iron; an element selected from the group consisting of 0.005% to 0.69% tin, 0.005% to 0.69% silver, and mixtures thereof; 0.05% to 0.50% zirconium; 0.02% to 0.14% vanadium; and the balance copper, said alloy characterized by having a refined grain size and improved mechanical properties at elevated temperatures.

2. The aluminum bronze alloy of claim 1, wherein said alloy has a percent elongation above 15% throughout the entire temperature range up to 1600 F. and has a tensile strength above 20,000 psi. at temperatures up to 1100 F.

3. The aluminum bronze alloy of claim 1, wherein said alloy consists essentially by weight of 6.00% to 6.75% aluminum, 2.00% to 2.40% iron, 0.10% to 0.25% zirconium, 0.05% to 0.12% vanadium, 0.01%; to 0.36% of an element selected from the group consisting of tin, silver and mixtures thereof, and the balance copper, said alloy characterized by having a refined grain size and improved mechanical properties at elevated temperatures.

4. The aluminum bronze alloy of claim 1, wherein the aluminum is present in a ratio of about 3 to 1 with respect to the iron.

References Cited UNITED STATES PATENTS 2,829,969 4/1958 Klement 75-162 X 3,330,653 7/1967 Paces et al. 75153 3,253,911 5/1966 Cairns 75161 X 2,059,560 11/1936 Corson 75154 2,136,918 11/1938 Hensel et a1. 75154 2,829,968 4/1958 Klement 75162 X CHARLES N. LOVELL, Primary Examiner US. 01. X.R. 7s 1s3, 162 

